(a) Technical Field
The present invention provides a polyamide resin composition that shows superior mechanical strength and heat resistance as well as improved glycol resistance and visibility maintenance, thus being useful in such a field that requires the aforementioned properties, for example in an automobile coolant reservoir tank.
(b) Background Art
In general, polyamide resin composition has superior mechanical property, heat resistance and drug resistance among various crystalline resins. Desired properties of polyamide resin composition may be achieved by addition of inorganic filling material such as glass fiber, carbon fiber, talc, wollastonite, calcium carbonate and barium sulfate. Further, physical and chemical resistance may be increased by addition of various functional additives. In addition, polyamide resin composition has superior processability, light weight, various and convenient design effect. Thus, it has been widely applied to various industrial fields such as automobile, ship and airplanes.
Polyamide 66 resin has been used to prepare a tank for supplementing an aqueous solution containing an anti-freezing solution (e.g., 50 vol %) of automobile engine cooling radiator. Polyamide 66 resin, however, shows a relatively high equilibrium moisture absorption and tends to undergo primary hydrolysis due to hot water (heated cooling water). The hydrolysis causes cleavage in intermolecular hydrogen bonding, producing molecules with lower molecular weight. On the other hand, ethylene glycol, which is a main ingredient of an anti-freezing solution contained in cooling water, causes glycolysis, converting amide group in polyamide resin into a compound having primary amine group and an ester compound having β-hydroxyethyl group. The thus-produced ultra-low-molecular-weight molecules decrease intermolecular binding and increase gaps between resin molecules, thereby inducing light scattering and lowering light transmittance and deteriorating visibility.
Further, pigments such as green dyes added in an anti-freezing solution are repeatedly pigmented onto the inner wall of cooler supplementing tank in a standstill state where heated cooling water is stationary. This may make it difficult to estimate the exact water level or may even lead to misread as if the tank is filled with a certain level of cooling water.
The aforementioned decrease in tank visibility or misreading of water level may prevent cooling water from being supplemented at the right time, thereby causing engine overheat or engine stop.
Researches have been made to improve the visibility of polyamide 66 resin such as heat resistance, glycol resistance and pigmentation resistance and achieved the improvement, to some extent, in its initial visibility and initial light transmittance. They, however, have not improved visibility maintenance with regard to heat resistance, anti-freezing solution resistance and pigmentation resistance.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.